Researchers have used mice to pinpoint what goes wrong in aneuploidy. Aneuploidy describes genetic disorders affecting chromosomes, usually resulting in an extra chromosome. Such disorders include Down syndrome and Edwards syndrome, and often cause pregnancy loss.

The researchers were looking at mutations of a particular gene in mice, to determine its role in colon cancer development. However, during the study they noticed that the mice carrying one copy of a mutation in the Bub1 gene had fewer offspring.

Further studies found that this effect was confined to female mice. If a mother’s egg had a mutation in one of the copies of Bub1 then she was more likely to have fewer offspring that survived until birth. They also found that the mutation was more harmful the older the mice were, which is the same for aneuploidy in humans.

Bub-1 works as a checkpoint in cell division, controlling the spindles which pull the chromosomes apart during cell division. It is likely that the mutation disrupts this process, resulting in extra chromosomes in the egg cells. Further tests will study the mutation in more detail to see if this is the case, and whether the mutation is present in humans.